1. Field of the Invention
The present invention is directed to tissue expander devices which are temporarily surgically implanted beneath the skin and subcutaneous layer for the purpose of creating a skin flap or enlargement. More particularly, the present invention is directed to an improved tissue expander device of the type which incorporates an injection reservoir within an inflatable shell of the tissue expander device itself.
2. Brief Description of the Prior Art
The prior art is well aware of tissue expander devices which are temporarily implanted beneath the skin and subcutaneous tissue of humans or domestic animals, and which may be gradually inflated by injection of saline (or similar liquids) for the purpose of causing the growth of a skin flap or enlargement. For a detailed description of such tissue expanders, reference is made to U.S. Pat. No. 4,217,889. Briefly summarized, such tissue expanders comprise a surgically implantable inflatable bag or shell into which the liquid is introduced to gradually enlarge the shell and thereby to cause the desired skin enlargement or flap formation. After the skin flap has formed, the shell is surgically removed. The skin flap is either used, after severance, for purposes of plastic surgery in other parts of the body, or accommodates a permanent implantation directly beneath the flap. Neither the manner of using the skin flap, nor the permanent implants, form part of the present invention.
For medically self-evident reasons, the temporarily implantable inflatable tissue expander shell must not leak, and must not be punctured to form a leak, when, from time to time, additional liquid is introduced into the shell. In some situations, liquid must even be withdrawn from the shell without causing a leak. Such addition or withdrawal of liquid is accomplished, in accordance with standard practice in the art, through a substantially non-expandable bioimplantable injection button or reservoir, which is self-sealing to punctures by a hypodermic needle. Varying constructions of injection buttons or reservoirs are described in U.S. Pat. Nos. 4,190,040 and 4,428,364.
Generally speaking, the injection button or reservoir is connected to the inflatable shell with a thin temporarily bioimplantable tube. Such structures having a "remote valve" are described, for example, in U.S. Pat. Nos. 4,217,889 and 4,190,040.
In an alternative construction of tissue expander devices, the injection reservoir is incorporated in the interior of the expandable shell. Such a tissue expander having a "self-contained" valve is described in U.S. Pat. No. 4,428,364. An advantage of this "self-contained" construction is that the entire tissue expander device is more compact, so that surgical implantation is simplified. However, in tissue expanders of this type, the surgeon usually has some difficulty in finding, for the purpose of inserting a hypodermic needle, the injection reservoir. Under these circumstances, it is difficult to be certain that only the injection reservoir, rather than the thin inflatable shell of the tissue expander, is pierced by the needle. In order to enable the surgeon to find the injection reservoir located beneath the apex of the inflatable shell, a palpation ring is provided in the prior art. The palpation ring, which is also implanted beneath the skin to surround the top portion of the injection reservoir, is then detected by the surgeon, and the hypodermic needle is inserted substantially in the center of the skin area located above the palpation ring.
A serious disadvantage of the above-summarized state-of-the-art tissue expanders having a "self-contained" valve is that the palpation ring tends to negatively affect the overlying tissue. Furthermore, even with the palpation ring, the injection reservoir is often hard to find, so that accidental puncture of the inflatable thin shell of the tissue expander is relatively common. Still further, the thin inflatable shell or bag has a tendency during implantation, and therafter, to fold over itself. Consequently, in the state-of-the-art tissue expanders having "self-contained" valves, a portion of the thin bag may actually be disposed above the injection reservoir. In such a case, of course, insertion of the hypodermic needle, even in the desired location in the center of the palpation ring, necessarily results in puncture of the inflatable shell.
In light of the foregoing, there is a definite need in tha art for an improved tissue expander device having a self-contained valve which avoids the foregoing disadvantages. The present invention provides such an improved tissue expander.